This project involves in vitro experiments using epithelial and connective tissue cells from human twins of all ages, as well as in vivo evaluation of the periodontal status and microbiologic picture of adult twins and their spouses. The overall aim is to elucidate the importance of genetic factors in the susceptibility of humans to microbially-elicited periodontal pathology. The classical human twin model, used for decades in medical research, has been utilized but seldom in dentistry. Comparisons of within and among twin pair variability yield information regarding heritable traits, since monozygotic identical twins have all of their genes in common, while dizygotic fraternal twins share only 50% of their genes. Correlation of environmental factors with periodontal phenotype may also be made using monozygotic co-twins as genetic controls for each other. We have recently demonstrated the feasibility of exploiting the classical twin paradigm for ideally controlled in vitro studies. We propose to exploit the Florida Twins Registry, which now comprises both monozygotic (MZ) and dizygotic (DZ) twins for a total of ca. 175 pairs. These twins, ranging in age from children to late middle-aged dentulous individuals, will be clinically documented for periodontal status. Subgingival plaque from healthy and periodontally diseased twins will be analyzed for bacterial composition. Specimens of saliva and serum from twins will be stored cryogenically for future studies. Explants of marginal gingiva from twin volunteers will be used to obtain and propagate gingival fibroblasts and epithelial cells from twins exhibiting varying degrees of periodontal pathology, and from healthy gingivae. The responses of twins' cells to in vitro challenges by sonicates of various putatively pathogenic microorganisms will be measured and compared by established statistical methods in the twin paradigm. Responses to such challenges will also be assessed with regard to subject age, race, sex, and periodontal -health status, as well as other environmental factors. These twin studies should lead us to fresh enlightenments concerning the role of heredity in human susceptibility to inflammatory disorders of the tooth-supporting structures.